it is fairly easy nowadays to pick up a wireless signal for free from neighbors or even going to Starbucks and the like for that matter. The signal won't be as strong or reliable as your own but free is free and you'd be surprised what some people have done using other people's wireless connections.
I know *lots* of people who do that, even though they know it's illegal to hop onto someone else's wireless.
BUT...here's what I'm thinking: Most people know about the traces left on their own computer.....and Steven had enough internet knowledge (SL Tribune website, Matchbin, etc) to know that traces would be left on HIS computer.
THAT, to me, explains why he used the library's computers rather than taking his notebook to McDonald's and using their WiFi.